Knowledge What is a paint or coating system?
A coating is a system that can be applied as a layer or a film to a suitable substrate. Coatings are used to protect all manner of components against damaging effects from the surrounding environment and to produce a finish that needs little maintenance and/or to give the desired decorative or cosmetic effect.
Where are coating systems used?
The single greatest consumer of the total world production of paint is the building and construction industries, other large areas of industrial painting are vehicles, marine, furniture, printing inks, and foil coatings.
Main requirements of a coating system
As mentioned above, the main purpose of a coating system is to provide protection against environment whether it is internal or external. There are four key properties which a coating system must have to be effective and these are as follows:
- To provide a barrier to prevent penetration of corrosive ions to the substrate
- To resist chemically aggressive environments
- To limit the effects of mechanical damage
- To provide a decorative appearance
Paint systems and their applications
Paint and coating systems are applied to all substrates to provide protection from their surrounding environments and to provide a cosmetic appearance.
Paint films create an insulating layer between metal surfaces and their environments. If the coating is sufficiently impermeable and is a continuous film without any breaks it will provide protection. However, in practice, many paint/coating systems contain breaks that allow the access of corrosion to form to the substrate. Protective paint coatings usually consist of three types of paints; a primer, an intermediate coat, and a topcoat.
The primer is the base for the coating system which is applied directly to a prepared substrate. Primers must have extremely good wet-out and adhesion properties. With a good corrosion protection system, the primer should contain corrosion inhibiting or passivating pigments which control the spread of corrosion.
Overall the primer must have the following properties:
- Good adhesion to the surface to be protected.
- A satisfactory bonding surface for subsequent coats.
- The ability to stifle or delay the spread of breaks in the coating.
- Sufficient chemical and weathering resistance by itself to protect the substrate for reasonable periods.
An intermediate coat, also referred to as the undercoat is applied over the primer. Its function is to build the overall coating thickness and place a barrier between the environment and primer. Thereby, providing protection against corrosion, the most common of which is water and oxygen. Paint can control the flow of water permeation to the substrate, and one or more of these layers can be applied depending on how aggressive the surrounding environment is.
Generally, the reasons for using an intermediate/undercoat are:
- Adhesion
- Topcoat problems during application
- Film thickness, permeation, and chemical resistance
A topcoat can be used to finish the system and its usual requirements are to provide general protection against the environment and is resistant to fading, loss of gloss and other effects caused by weathering.